(1) Field of the Invention
The present invention relates to an alternating current electric recording process. More particularly, the present invention relates to an alternating current electric recording process in which by applying as electric recording signals high frequency alternating current or asymmetric alternating current signals formed by amplifying and modulating image signals and using an electrostatic recording material comprising an electroconductive substrate having a specific multilayer distribution structure, such problems as blurring, tailing and fogging can be effectively eliminated and recorded images excellent in the density and sharpness can be formed without substantial influences of the humidity in the recording atmosphere.
(2) Description of the Prior Art
As the conventional electric recording process, there is known a so-called electrostatic recording process comprising moving relatively a pair of a recording electrode and a counter electrode and an electrostatic recording material electrically connected between the two electrodes, applying an electric recording signal between the two electrodes to form an electrostatic latent image on the electrostatic recording material, developing the so formed electrostatic latent image with a developer and, if desired, fixing the developed image.
In general, direct current signals are used as the electric recording signal to be applied in this known electrostatic recording process. However, a high-voltage direct current applied to a recording stylus not only forms a latent image on the recording surface but also causes such problems as so-called "blurring", "tailing" and "fogging". For example, Messrs. Haneda, Ito and Hashigami teach that simultaneously with formation of a latent image as mentioned above, charges of the opposite polarity, which are deemed to be due to influences of induction or electric force lines, are accumulated in the vicinity of the latent image to cause "blurring", when the recording stylus is moved, charges accumulated on the recording stylus and other recording equipments are applied and transferred to the recording surface to cause "tailing". Because of the potential forming the latent image, the entire recording surface is charged at the same polarity as that of the latent image, though the intensity of charging is lower than in the latent image and this charging results in "fogging" (see the Journal of the Electrophotographic Association, April 1970, pages 37 to 43). Accordingly, in a final image obtained by the electrostatic recording process using a high-voltage direct current as the electric recording signal, the resolving power is reduced by the above-mentioned undesirable phenomena such as blurring, tailing and fogging and the image becomes obscure. Further, when recording is carried out at a high speed, namely when the relative scanning speed of the recording stylus and recording material is enhanced, the above defect becomes especially conspicuous.
Methods using as electric recording signals high frequency signals formed by amplifying and modulating image signals have already been proposed in Japanese Patent Publications Nos. 33516/71 and 21311/65. It is taught that according to the method disclosed in the former patent publication, since charges of different polarities are alternately applied, charges oriented in the vertical direction of a recording paper are not formed and a powdery developer is uniformly stuck to either the peripheral portion or the central portion of a latent image on the recording paper, whereby the edge effect is eliminated and an image of good quality is obtained. The latter patent publication discloses that according to the claimed alternating current recording method, the entire circuit structure can be simplified, any developer can be used irrespective of the polarity of the toner and an image having a sufficient resolving power is obtained.
Images obtained according to the known alternating current recording methods, however, are still insufficient in the density and sharpness, and therefore, these alternating current recording methods have not been satisfactory.
Still further, the known electrostatic recording methods are defective in that electrostatic recording materials are readily influenced by the humidity in the recording atmosphere. In general, recording materials comprising an electroconductive substrate and a dielectric layer formed thereon have been used as electrostatic recording materials, but in each of the known electroconductive layers, the electroconductivity is considerably influenced by the humidity and no sufficient conductivity can be obtained unless under considerably high humidity conditions. Accordingly, in the conventional electrostatic recording materials, it is difficult to charge the dielectric layer to a sufficient recording voltage under low humidity conditions and hence, it is ordinarily difficult to form images having a high density. This tendency is especially conspicuous when such electrostatic recording materials are used for the above-mentioned alternating current recording process and serious problems arise with respect to the absolute density and contrast in recorded images.